I was reminded last week of what the war in Afghanistan means. I met a local mother whose son had just left to fight there. She was calm and proud but, naturally, anxious. She made a very humble request: a network of contacts with other parents.

I have deeper worries. Our Afghan war has now lasted almost twice the length of the First World War (there was also a quarter century of civil war and conflict before 2001). Despite the heroism of British troops (and the Americans, Danes and a few others) there is no ‘victory’ in sight (whatever ‘victory’ means).

The original target, Bin Laden and his terrorist friends, escaped into Pakistan years ago. Terrorists have lots of other potential boltholes. The awful Taliban were driven from power but are now growing again in opposition. Our "allies" in government comprise warlords and gangsters. The heroin trade has boomed, not stopped.

More troops, helicopters and equipment would, no doubt, help to win a skirmish here and there. But who will pay? The Government is in no position to sign big cheques. The £3 billion or more we spent in Iraq and similar amounts in Afghanistan have already weakened the budget badly. New money would have to come from cuts elsewhere including the long, expensive shopping list of ships and planes favoured by the excessive numbers of military top brass.

We must be realistic too about our war aims. We cannot just walk away from Afghanistan, but cannot expect to ‘win’ through set piece battles. The sad history of failed foreign armies in Afghanistan – from the British Empire to Russia – is a cautionary tale. A modest level of stability policed by the semi-democratic Afghan government is achievable followed by withdrawal.

There has to be an early exit strategy. Otherwise our troops will be sucked into a deadly quagmire.